Assessment of protein nutritional status.

An evaluation of protein status can be approached by use of anthropometric, clinical, and biochemical data, either singly or in combination, and further aided with dietary data. Each of these approaches has advantages and limitations. Biochemical evaluation has the potential of being the most objective and quantitative. Indicators that have been or might be used include plasma hormone responses to reduced protein intake, plasma levels of specific proteins or specific amino acids, urinary excretion of specific amino acids and other nitrogen-containing compounds, anthropometric and physical measurements of body muscle mass, and functional tests of muscle strength. Several measurements can be combined to produce nutritional indices of broader potential value. The importance of concomitant infection and inflammation, with its many effects on protein metabolism, cannot be ignored in making these assessments. Unfortunately, no single test or group of tests can be recommended at this time as a routine and reliable indicator of protein status. Nonetheless, our increasing knowledge of the metabolism and functions of proteins, together with the recent use of noninvasive stable isotope techniques and of sophisticated physicochemical measurements, provides encouragement that more appropriate indicators are in the offing.